部分代码
Place place = em.createQuery("from Place where name = :name", Place.class)
.setParameter("name", name)
.setFlushMode(FlushModeType.COMMIT) // <-- yay!
.getSingleResult();
示例代码如下:
@Entity @Table(name="place") @Immutable
public class Place {
private Long _id;
private String _name;
@Id @GeneratedValue
public Long getId() { return _id; }
public void setId(Long id) { _id = id; }
@Basic(optional=false) @Column(name="name", length=700,
updatable=false, nullable=false, unique=true,
columnDefinition="varchar(700) character set 'ascii' not null")
public String getName() { return _name; }
public void setName(String name) { _name = name; }
@Override
public boolean equals(Object o) { /* ... */ }
@Override
public int hashCode() { return getName().hashCode(); }
}
我的测试代码生成100000个随机地名并插入它们。然后随机查询其中5000的名字。Name列上有一个索引。
Place place = em.createQuery(
"select p from Place p where p.name = :name", Place.class)
.setParameter("name", name)
.getSingleResult();
在另一个随机选择数据:
PreparedStatement ps = c.prepareStatement(
"select id, name from place where name = ?");
ps.setString(1, name);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
Place place = new Place();
place.setId(rs.getLong(1));
place.setName(rs.getString(2));
}
rs.close();
ps.close();
下面的所有结果平均超过5000次查询
Seconds/Query Approach
0.000160s JDBC
0.000286s Hibernate calling clear() after import and every 100 queries
0.000653s Hibernate calling clear() once after the import
0.012533s Hibernate w/o calling clear() at all
0.000292s Hibernate w/o calling clear(), and with flush-mode COMMIT
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